Studies OH Sponges. II— IV. 487 



to keep up the current of water and with it the food, as they do by 

 means of the flagellated collar-cells. The more new water eomes in 

 contact with those cells which take in the food-particles the more fully 

 the Sponge may develop itself. Now it is evident that those specimens 

 which hang on the keel of vessels and are thus dragged through the 

 water as the vessel moves must, at least may be in a favourable condi- 

 tion for their development. I have therefore no doubt that the (passive) 

 movement through the water is the origin of its gigantic 

 size. As I was oceupied, some years ago, in studying the oyster-cul- 

 ture in Holland at Bergen-op-Zoom and Yerseke I foimd Calcareous 

 Sponges (for the first time on our coasts) in the tanks where the young 

 oysters are kept. These animals are carefully spread on a kind of frame- 

 work, which is left swimming in the water. On the same framework 

 and on the little oysters, hanging downwards as they grow through the 

 raeshes a great quantity of Sycons were to be found. These Sycons 

 belong to Haeckel's Sycandra ciliata and coronata ^ and reach an enor- 

 mous size. As the water in the big tanks is changed , I believe twice a 

 day, so also this circumstance may be a favourable factor for the size of 

 the Sponges. Not only do they develop rather well in the tanks as re- 

 gards the size, but they seem also to grow very quickly. As people 

 believe that these Sponges are dangerous for the oysters so every week 

 or every fortnight the frames are lifted and those Sycons are taken away 

 which by their size attract notice. I saw often specimens of about 65 mm. 

 Supposing that these people only take away specimens of more than 

 30 mm, then even we may say that the Sycons grow from 30 to 

 65 mm (in length) in half a month. 



Returning to our Leucoma aspera we have more questions to solve. 

 Why is the roughness in the typical L. aspera gone ? There may be 

 two reasons for this. In the first place it is possible that the augmented 

 pression and friction of the water diminuished the angle which the rods 

 make with the axis of the Sponge. But another explanation may be 

 given still. According to the most recent investigations it is highly 

 probable that in Sponges the cells of the surface as well as those ecto- 

 dermic cells which line the subdermal cavi ties, if present, andtheinhalant 

 canals take in food-particles. If this is true it is of great importance for 

 fixed animals to keep hold of the food that comes in their neigborhood, 

 and thus the protruding spicules may have the function, at least partly, 



1 I believe that both are identical and shall call them Sycon ciliattim (Fabr.) 

 Lbkn. 



